js实现简洁大方的二级下拉菜单效果代码

本文实例讲述了js实现简洁大方的二级下拉菜单效果代码。分享给大家供大家参考。具体如下：

这是一款简洁大方的二级下拉菜单，菜单的颜色自己根据需要重新定义吧，这里仅给大家提供一种制作二级菜单的思路，整体效果看上去相当实用，下拉导航菜单也是大家比较常用的。

运行效果截图如下：

在线演示地址如下：

http://demo.jb51.net/js/2015/js-simple-2level-show-down-menu-codes/

具体代码如下：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>简洁大方的二级下拉菜单</title>
<meta http-equiv="content-type" content="text/html;charset=gb2312">
<style type="text/css">
*{margin:0;padding:0;font-style:normal;font-family:宋体;}
body{text-align:center;font-size:14px;}
#content{margin:0 auto;width:600px;}
#content #nav{background:#006400;height:32px;margin-top:10px;}
#content #nav ul{list-style:none;}
#content #nav ul li{float:left;width:100px;line-height:32px;position:relative;}
#nav div{width:100px;position:absolute;left:0px;padding-bottom:0px;background:#006400;float:left;height:0;overflow:hidden;}
#content #nav li .a{text-decoration:none;color:#00CD00;line-height:32px;display:block;border-right:1px solid #009800;}
#nav div a{text-decoration:none;color:#00CD00;line-height:26px;display:block;}
#nav div a:hover{background:#005400;}
</style>
</head>
<body>
<div id="content">
 <div id="nav">
  <ul id="supnav">
   <li><a href="#" class="a">菜单项1</a>
    <div>
     <a href="#">菜单测试1</a>
     <a href="#">菜单测试1</a>
     <a href="#">菜单测试1</a>
    </div>
   </li>
   <li><a href="#" class="a">菜单项2</a>
    <div>
     <a href="#">菜单测试2</a>
     <a href="#">菜单测试2</a>
     <a href="#">菜单测试2</a>
    </div>
   </li>
   <li><a href="#" class="a">菜单项3</a>
    <div>
     <a href="#">菜单测试3</a>
     <a href="#">菜单测试3</a>
     <a href="#">菜单测试3</a>
     <a href="#">菜单测试3</a>
     <a href="#">菜单测试3</a>
    </div>
   </li>
   <li><a href="#" class="a">菜单项4</a>
    <div>
     <a href="#">菜单测试4</a>
     <a href="#">菜单测试4</a>
     <a href="#">菜单测试4</a>
    </div>
   </li>
   <li><a href="#" class="a">菜单项5</a>
    <div>
     <a href="#">菜单测试5</a>
     <a href="#">菜单测试5</a>
     <a href="#">菜单测试5</a>
     <a href="#">菜单测试5</a>
    </div>
   </li>
   <li><a href="#" class="a">菜单项6</a>
    <div>
     <a href="#">菜单测试6</a>
     <a href="#">菜单测试6</a>
     <a href="#">菜单测试6</a>
    </div>
   </li>
  </ul>
 </div>
</div>
<script type="text/javascript">
var supnav=document.getElementById("supnav");
var nav=document.getElementById("nav");
var btns=document.getElementsByTagName("li");
var subnavs=nav.getElementsByTagName("div");
var paddingbottom=20;
var defaultHeight=0;
function drop(obj,ivalue){
 var a=obj.offsetHeight;
 var speed=(ivalue-obj.offsetHeight)/8;
 a+=Math.floor(speed);
 obj.style.height=a+"px";
}
window.onload=function(){
 for(var i=0;i<btns.length;i++){
  btns[i].index=i;
  btns[i].onmouseover=function(){
   var osubnav=subnavs[this.index];
   var sublinks=osubnav.getElementsByTagName("a");
   if(osubnav.firstChild.tagName==undefined){
    var itarheight=parseInt(osubnav.childNodes[1].offsetHeight)*sublinks.length+paddingbottom;
   }else{
    var itarheight=parseInt(osubnav.firstChild.offsetHeight)*sublinks.length+paddingbottom;
   }
   clearInterval(this.itimer);
   this.itimer=setInterval(function(){drop(osubnav,itarheight);},30);
  }
  btns[i].onmouseout=function(){
   var osubnav=subnavs[this.index];
   clearInterval(this.itimer);
   this.itimer=setInterval(function(){drop(osubnav,defaultHeight);},30);
  }
 }
}
</script>
</body>
</html>

希望本文所述对大家的javascript程序设计有所帮助。